Kenyan Internal Security Minister George Saitoti has been killed in a helicopter crash, officials say.
Mr Saitoti and his deputy, Orwa Ojode, died when the aircraft went down west of Nairobi. President Mwai Kibaki has declared three days of mourning.
There is no word on the cause of the crash, in which six people were killed, including bodyguards and pilots.
Mr Saitoti, a former vice-president, had been planning to run in a forthcoming presidential poll.
The 66-year-old was on his way to a security meeting when his helicopter crashed on Sunday morning.
An journalist for AFP news agency saw six charred bodies being removed from the wreckage.
Another reporter at the scene says debris of the burnt-out police helicopter were strewn in the brush.
Prime Minister Raila Odinga, speaking at the site, described the deaths as a "great tragedy", and promised a thorough investigation into the cause of the crash.
George Saitoti had been a key figure in Kenyan politics, holding a number of senior ministerial posts over the last 30 years and becoming the country's longest-serving vice-president.
The professor of mathematics joined Daniel arap Moi's government as a finance minister in 1983, going on to become his vice-president in 1988.
He briefly stepped down as education minister in 1996 over accusations he was involved in the Goldenberg financial scandal, but was reinstated when a Kenyan court ruled he should not be charged.
After years as a senior member in the long-dominant Kanu party, Mr Saitoti joined the current president Mwai Kibaki's National Alliance of Kenya in 2002.
As Internal Security Minister under Mr Kibaki, he was a leading government voice against the Somali militant group al-Shabab.
Kenyan troops have been fighting al-Shabab in Somalia since they sent troops into the country last October.
The militants have killed several people in a string of grenade attacks in various parts of Kenya, including Nairobi.
Mr Saitoti announced he would stand for the presidency last November.
No date for the presidential election has so far been set. Mr Kibaki's mandate ends in January 2013.
Prime Minister Odinga - a rival of both Mr Kibaki and Mr Saitoti - is also to stand for president.
The last presidential election, in December 2007, was followed by a wave of ethnic and political violence in which about 1,500 were killed.